As an advanced standard of IEEE802.11n which is a radio LAN (Local area network) standard that has been widely put into use, an IEEE802.11ac standard has been developed by the IEEE (The Institute of Electrical and Electronics Engineers, Inc.). Currently, standardization efforts for HEW (High efficiency wireless LAN) are to be conducted as a successive standard of IEEE802.11n/ac. Differently from the past radio LAN standards, not only improvement in peak throughput but also improvement in user throughput are cited as main required conditions in the HEW standard. It is essential to introduce a highly efficient simultaneous multiplexing transmission scheme (access scheme) in order to improve the user throughput.
In standards before the standard of the IEE802.11n, an access scheme of an autonomous distributed control type called CSMA/CA (Carrier sense multiple access with collision avoidance) has been adopted as the access scheme. In the IEEE802.11ac, space division multiple access (SDMA) by a multi-user multiple-input multiple-output (MU-MIMO) technique is newly added.
The HEW standard is required to further improve the access scheme for improving the user throughput. As the highly efficient access scheme, there is Orthogonal Frequency Division Multiple Access (OFDMA). The OFDMA is a scheme for, by using characteristics of Orthogonal Frequency Division Multiplexing (OFDM) which allows enhancement in frequency efficiency by arranging a large number of orthogonal sub-carriers densely at intervals of a reciprocal of a signal duration, allocating any number of sub-carriers (or a frequency band composed of a group of contiguous sub-carriers) with good characteristics to each of radio reception apparatus in accordance with reception characteristics different in the radio reception apparatuses in multipath environments, and thereby further increasing substantial frequency efficiency. It is expected that the user throughput is improved by introducing the OFDMA to the HEW standard (NPL 1).